Matrix assisted laser desorption ionization (MALDI) mass spectrometry is a technique that provides minimal fragmentation and high sensitivity for the analysis of a wide variety of fragile and non-volatile compounds. MALDI is often combined with time-of-flight (TOF) mass spectrometry, FTICR, quadrupole ion trap, and triple quadrupole mass spectrometers, providing for detection of large molecular masses. These systems may be used to determine molecular weights of biomolecules and their fragment ions, monitor bioreactions, detect post-translational modifications, and perform protein and oligonucleotide sequencing, for tissue imaging, and many more applications.
The MALDI technique involves depositing the sample (analyte) and a matrix dissolved in a solvent as a spot on a sample plate. After the solvent has evaporated, the mixture of sample and matrix is left on the sample plate. The sample plate bearing the sample spots is inserted into the mass analyzer and the mass analyzer is typically pumped out to provide a vacuum environment before the sample at each spot is analyzed. The MALDI technique requires that a pulse from a laser irradiate the matrix and causes it to evaporate. The sample is carried with the matrix, ionized, and analyzed by the mass analyzer. Loading a sample plate into a mass analyzer and subsequently pumping the vacuum pressure mass spectrometer down to a pressure at which analysis can take place, typically takes several minutes.
Typically, operators handle the sample plate in a vertically orientated position, this vertical position being the position in which the sample plate is orientated when subjected to radiation by a laser. This orientation is not considered by operators to be natural, and consequently, in order to enable stable manual loading of the sample plate the sample plate is presented horizontally thus allowing a user to load and unload the sample plate with only one hand.
In addition, existing MALDI sample plate handling systems typically experience situations in which the sample plate exchange becomes jammed, stuck, dropped or lost. This is particularly the case for systems that utilize electro-mechanical or pneumatic gripping mechanisms which may lose contact with or disengage the sample plate due to power loss.
The sample plates are handled in an atmospheric environment, but prior to analysis are required to reside in a vacuum chamber of a mass analyzer, so mechanisms to pick the sample plate up and deliver the sample plate to the vacuum chamber are required. In addition, mechanisms are required to ensure that the sample plate can be positioned within the mass analyzer in a manner that is reliably repeatable. That is, in a manner that can be repeated such that one can be assured a sample plate is being positioned at the same location within the mass analyzer each time.
Sample plate delivery systems typically utilize at least two such mechanisms to accommodate the fact that the sample plate is picked up from an environment that is at atmospheric pressure and is required to be transferred through different pressure regions before arriving in the vicinity of vacuum chamber of mass analyzer. The mechanisms generally have fingers or a fork that grasp the sample plate along at least one edge of the sample plate, and may be robotic. But most have an additional adapter attached to accommodate the automated hand-off. Most vacuum sample plate systems use a drop stage and two stationary actuators to move a sample plate into a vacuum chamber. This transfer process provides room for error in reliability of repeatability, in that the position of the sample plate is not fixed along any axis throughout the process.